Current digital video transmission systems employ compressed streams of video and audio data. The compressed video consists of groups of inter-coded pictures, or for short, group of pictures. A group of pictures (GOP) is a mixture of intra-coded frames (intra-frame compressed images), or for short, I-frames, where each frame is compressed on its own, and inter-frame-compressed video sequences, where encoded motions between frames are used to gain additional compression due to image similarity between adjacent frames. This second mode of compression typically necessitates waiting for a stand-alone compressed frame before the decompression of a video sequence can begin. In a multi-program stream environment, different programs of video present these stand-alone frames (known in MPEG-2 standard as “key-frames” or “I-frames” ) at different points in time. Therefore switching from one program to another is delayed by at least the waiting time required for a stand-alone frame of the selected program to arrive. Subsequent processing to decompress the stream adds a further delay to the switching of programs. Currently, the most widely used video compression standard is MPEG-2, although similar compression methods are used in other video codecs (e.g. MPEG-4, H.264, WM9 etc.). Most of these methods share the shortcomings of video latency caused by inter-frame compression.
As a result, current compressed video delivery systems (e.g. set-top boxes) require a long delay time to assemble and display the first frame and subsequent motion-video of a newly selected video program. At the instant of switching to another video program, the decompression process must wait for a completely self-contained, compressed still-image (e.g. an I-frame in the MPEG-2 stream) of the selected video program, and/or accumulate sufficient bit-stream data to create a complete frame from non-I-frame data in the stream.
Data streams are not collected for other compressed video programs, as typically, there is only processing capability for a single compressed stream in prior art set-top boxes. An exception to this situation occurs where “live” picture-in-picture is an option of the system, but this does not address the problem of slow program acquisition, or graphically based program selection (described below). Another exception is the case where multiple parallel decoders decompress all video programs in parallel—real-time (e.g. cable company head-ends), but this solution is excessive in computation, hardware and cost when applied purely to handling video program changing in a home environment. MPEG-2 I-frames usually occur roughly once every half-second per broadcast video program. A group of pictures (GOP)” must contain at least one I-frame, and is the smallest unit of MPEG-2 video access. Therefore the period between GOPs limits fast switching, or scanning up/down video programs, and rapid browsing is thus prevented in current systems.
It is therefore desirable to invent a system and method for rapid successive viewing of selected digital video programs, which is fast, fairly seamless, and permits smoother transitions between digital video programs. It is also desirable to be able to simultaneously view multiple “thumbnail” representations of a group of programs, to enable graphic program selection from an on-screen palette.